Excel

https://en.wikipedia.org/wiki/Microsoft_Excel

Trick
http://www.exceltrick.com/

Functions
http://www.excelfunctions.net/

Easy
http://www.excel-easy.com/

Jet
https://exceljet.net/

Grid
http://www.ozgrid.com/

Mr
https://www.mrexcel.com

Lab
http://www.myexcelab.com

Videos Series
http://www.youtube.com/watch?v=OTz2PQ-CdJU
Excel / Basic / Videos
http://en.wikipedia.org/wiki/Microsoft_Excel
https://exceljet.net/
http://www.youtube.com/results?search_query=Microsoft+Excel+Tutorial+for+Beginners&aq=f
General Excel Tips
http://home.ubalt.edu/ntsbarsh/excel/excel.htm
http://www.newhorizons.com/courses/microsoft-office/excel.aspx
http://www.bmedia4tech.com/2013/11/15/139/Here-are-75-Excel-Shortcuts-tips-to-improve-your-skill